U.S. patent number 7,103,878 [Application Number 10/020,631] was granted by the patent office on 2006-09-05 for method and system to instrument virtual function calls.
This patent grant is currently assigned to Hewlett-Packard Development Company, L.P.. Invention is credited to Brian Fahs, Robert Hundt, Tara Krishnaswamy.
United States Patent |
7,103,878 |
Fahs , et al. |
September 5, 2006 |
Method and system to instrument virtual function calls
Abstract
A method and system for analyzing a virtual function. In one
embodiment, the present invention determines whether a virtual
table exists for a virtual function, and determines a call type for
the virtual function. In the present embodiment, provided the
virtual table is located, the present invention replaces an
existing address for the virtual function with a new address such
that the new address points to instrumentation code. In this
embodiment, upon a call to the virtual function, the present
invention loads the new address from the virtual table such that
execution is directed to the instrumentation code. The present
embodiment continues execution and executes the instrumentation
code such that control is delivered to the instrumentor.
Inventors: |
Fahs; Brian (Champaign, IL),
Hundt; Robert (Santa Clara, CA), Krishnaswamy; Tara
(Cupertino, CA) |
Assignee: |
Hewlett-Packard Development
Company, L.P. (Houston, TX)
|
Family
ID: |
21799708 |
Appl.
No.: |
10/020,631 |
Filed: |
December 13, 2001 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20030115584 A1 |
Jun 19, 2003 |
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Current U.S.
Class: |
717/130; 717/141;
712/E9.084; 714/E11.209 |
Current CPC
Class: |
G06F
11/3612 (20130101); G06F 9/449 (20180201); G06F
11/3644 (20130101) |
Current International
Class: |
G06F
9/44 (20060101); G06F 9/45 (20060101) |
Field of
Search: |
;717/100-169 ;701/1
;709/320 ;707/201 ;713/213 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Hollingsworth et al., MDL: a language and compiler for dynamic
program instrumentation, Parallel Architectures and Compilation
Techniques., 1997. Proceedings. 1997 International Conference on ,
Nov. 10-14, 1997, IEEE, pp. 201-212. cited by examiner .
Sloane, Generating dynamic program analysis tools, Software
Engineering Conference, 1997. Proceedings. 1997 Australian , Sep.
29-Oct. 2, 1997,IEEE, pp. 166-173. cited by examiner .
Rawnsley et al., A virtual instrument bus using network
programming, IEEE, May 1997 pp. 694-697 vol 1. cited by examiner
.
Kang et al., The method of developing Virtual Instrument Platform,
IEEE, Sep. 2000 pp. 64-67. cited by examiner .
Spoelder et al., Virtual instrumentation: a survey of standards and
their interrelation, IEEE, May 1997 pp. 676-681 vol. 1. cited by
examiner.
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Primary Examiner: Zhen; Wei
Assistant Examiner: Rampuria; Satish S.
Claims
The invention claimed is:
1. A computer-implemented method for analyzing a virtual function,
said method comprising: locating a virtual table for a virtual
function, said virtual table comprising a start address for said
virtual function; creating an instruction for said virtual
function, said instruction comprising a control transfer function
that directs execution to instrumentation code; rewriting said
virtual table with a modified virtual table comprising an address
for said instruction instead of said start address; loading said
address for said instruction upon determining that a call to said
virtual function is a virtual function call, thereby directing
execution to said instrumentation code; and executing said
instrumentation code to perform an instrumentation task for said
virtual function.
2. The computer-implemented method for analyzing a virtual function
as recited in claim 1 further comprising: performing a desired
instrumentation task; and resuming execution at said start address
previously contained in said virtual table.
3. The computer-implemented method for analyzing a virtual function
as recited in claim 1 further comprising: overwriting said
instrumentation code with instrumentation code which performs a
desired instrumentation task; and providing an instruction at the
end of said instrumentation code wherein said instruction points
back to said start address previously contained in said virtual
table.
4. The computer-implemented method for analyzing a virtual function
as recited in claim 1 further comprising: determining from which
location said virtual function has been called.
5. The computer-implemented method for analyzing a virtual function
as recited in claim 1 further comprising: maintaining a mapping
between said start address for said virtual function and said
address for said instruction.
6. The computer-implemented method for analyzing a virtual function
as recited in claim 1 wherein said instruction contains only a
single breakpoint instruction.
7. A computer-readable storage medium embodying instructions that
cause a computer to perform a method for analyzing a virtual
function, said method comprising: locating a virtual table for a
virtual function, said virtual table comprising a start address for
said virtual function; creating an instruction for said virtual
function, said instruction comprising a control transfer function
that directs execution to instrumentation code; rewriting said
virtual table with a modified virtual table comprising an address
for said instruction instead of said start address; loading said
address for said instruction upon determining that a call to said
virtual function is a virtual function call, thereby directing
execution to said instrumentation code; and executing said
instrumentation code to perform an instrumentation task for said
virtual function.
8. The computer-readable storage medium of claim 7 further
comprising instructions that cause said computer to perform said
method further comprising: performing a desired instrumentation
task; and resuming execution at said start address previously
contained in said virtual table.
9. The computer-readable storage medium of claim 7 further
comprising instructions that cause said computer to perform said
method further comprising: overwriting said instrumentation code
with instrumentation code which performs a desired instrumentation
task; and providing an instruction at the end of said
instrumentation code wherein said instruction points back to said
start address previously contained in said virtual table.
10. The computer-readable storage medium of claim 7 further
comprising instructions that cause said computer to perform said
method further comprising: determining from which location said
virtual function has been called.
11. The computer-readable storage medium of claim 7 further
comprising instructions that cause said computer to perform said
method further comprising: maintaining a mapping between said start
address for said virtual function and said address for said
instruction.
12. An apparatus for analyzing a virtual function, said apparatus
comprising: means for locating a virtual table for a virtual
function, said virtual table comprising a start address for said
virtual function; means for creating an instruction for said
virtual function, said instruction comprising a control transfer
function that directs execution to instrumentation code; means for
rewriting said virtual table with a modified virtual table
comprising an address for said instruction instead of said start
address; means for loading said address for said instruction upon
determining that a call to said virtual function is a virtual
function call, thereby directing execution to said instrumentation
code; and means for executing said instrumentation code to perform
an instrumentation task for said virtual function.
13. The apparatus of claim 12 for analyzing a virtual function,
said apparatus further comprising: means for performing a desired
instrumentation task by said instrumentor; and means for resuming
execution by said instrumentor at said start address previously
contained in said virtual table.
14. The apparatus of claim 12 for analyzing a virtual function,
said apparatus further comprising: means for overwriting said
instrumentation code with instrumentation code which performs a
desired instrumentation task; and means for providing an
instruction at the end of said instrumentation code wherein said
instruction points back to said start address previously contained
in said virtual table.
15. The apparatus of claim 12 for analyzing a virtual function,
said apparatus further comprising: means for determining from which
location said virtual function has been called.
16. The apparatus of claim 12 for analyzing a virtual function,
said apparatus further comprising: means for maintaining a mapping
between said start address for said virtual function and said new
address for said virtual function.
Description
TECHNICAL FIELD
The present claimed invention relates to instrumentation of a
computer program. More specifically, the present claimed invention
relates to instrumenting of virtual functions.
BACKGROUND ART
Over recent years, the computing community developed a strong set
of tools and methods used to analyze and monitor run-time behavior
of a program. One type of performance analysis is referred to as
instrumentation. Measurements such as basic-block coverage and
function invocation counting can be accurately made using
instrumentation. One specific type of code instrumentation is
referred to as dynamic binary instrumentation. Dynamic binary
instrumentation allows program instructions to be changed
on-the-fly. Additionally, dynamic binary instrumentation, as
opposed to static instrumentation, is performed at run-time of a
program and only instruments those parts of an executable that are
actually executed. This minimizes the overhead imposed by the
instrumentation process itself. Furthermore, performance analysis
tools based on dynamic binary instrumentation require no special
preparation of an executable such as, for example, a modified build
or link process.
Certain modern programming languages such as, for example, C++
offer the ability to inherit so called derived objects from other
base objects. This concept is commonly known as inheritance in the
object oriented programming domain. Often, these base and/or
derived objects use what are known as virtual functions. Hence, it
is possible in certain instances to make a call to a virtual
function. To accomplish this, the compiler generates an array of
function pointers, known as a virtual table, for each object type
that contains at least one virtual function. During the virtual
function call, this virtual table is indexed to obtain a function
pointer, and then an indirect call is made using that function
pointer. Such tables must be created because the actual function
call made may not be determinable at compile time. Additionally, it
is not possible, at present, to readily instrument or analyze such
virtual function calls.
Furthermore, programmers are often interested in deciphering the
type of call which is made to a function such as, for example, a
virtual function. More specifically, various function call types
such as, for example, direct function calls, indirect function
calls, and virtual function calls have differing costs associated
therewith. That is, the various function calls differ in terms of
the cycles and/or instructions executed in performing the function
call. Unfortunately, at present, there is no current method for
determining the call type for a virtual function.
Thus, a need has arisen for a method and system for analyzing a
virtual function including determining the type of call made to the
virtual function.
DISCLOSURE OF THE INVENTION
The present invention provides a method and system for method and
system for instrumenting a virtual function including determining
the type of call made to the virtual function.
Specifically, in one method embodiment, the present invention
determines a call type for a virtual function. The present
embodiment then locates a virtual table corresponding to a virtual
function and replaces an existing address for the virtual function
with a new address for the virtual function in the virtual table.
In this embodiment, the new address points to instrumentation code.
Upon a call to the virtual function, the present embodiment then
loads the new address from the virtual table such that execution is
directed to the instrumentation code. The present embodiment
continues execution and executes the instrumentation code and
delivers control to an instrumenting application.
These and other technical advantages of the present invention will
no doubt become obvious to those of ordinary skill in the art after
having read the following detailed description of the preferred
embodiments which are illustrated in the various drawing
figures.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, which are incorporated in and form a
part of this specification, illustrate embodiments of the invention
and, together with the description, serve to explain the principles
of the invention:
FIG. 1 is a schematic diagram of an exemplary computer system used
to perform steps of the present method in accordance with various
embodiments of the present claimed invention.
FIG. 2 is a flow chart of steps performed to determine a call type
of a virtual function in accordance with one embodiment of the
present claimed invention.
FIG. 3 is a flow chart of steps performed in performing
instrumentation of a virtual function in accordance with one
embodiment of the present claimed invention.
FIG. 4 is a flow chart of steps performed in instrumentation of a
virtual function by readdressing a virtual table in accordance with
one embodiment of the present claimed invention.
FIG. 5 is a flow chart of steps performed in instrumentation of a
virtual function by readdressing of a virtual table and controlling
execution via an instrumentor in accordance with one embodiment of
the present claimed invention.
FIG. 6 is a flow chart of steps performed in instrumentation of a
virtual function by readdressing of a virtual table and controlling
execution via a target process in accordance with one embodiment of
the present claimed invention.
FIG. 7 is a flow chart of steps performed to determine a call type
of a virtual function and to determine from which the virtual
function has been called in accordance with one embodiment of the
present claimed invention.
FIG. 8 is a flow chart of steps performed in instrumentation of a
virtual function by readdressing a virtual table and maintaining a
mapping of virtual tables addresses in accordance with one
embodiment of the present claimed invention.
The drawings referred to in this description should be understood
as not being drawn to scale except if specifically noted.
BEST MODES FOR CARRYING OUT THE INVENTION
Reference will now be made in detail to the preferred embodiments
of the invention, examples of which are illustrated in the
accompanying drawings. While the invention will be described in
conjunction with the preferred embodiments, it will be understood
that they are not intended to limit the invention to these
embodiments. On the contrary, the invention is intended to cover
alternatives, modifications and equivalents, which may be included
within the spirit and scope of the invention as defined by the
appended claims. Furthermore, in the following detailed description
of the present invention, numerous specific details are set forth
in order to provide a thorough understanding of the present
invention. However, it will be obvious to one of ordinary skill in
the art that the present invention may be practiced without these
specific details. In other instances, well known methods,
procedures, components, and circuits have not been described in
detail as not to unnecessarily obscure aspects of the present
invention.
It should be borne in mind, however, that all of these and similar
terms are to be associated with the appropriate physical quantities
and are merely convenient labels applied to these quantities.
Unless specifically stated otherwise as apparent from the following
discussions, it is appreciated that throughout the present
invention, discussions utilizing terms such as "determining",
"instrumenting", "overwriting", "executing", "performing", or the
like, refer to the actions and processes of a computer system, or
similar electronic computing device. The computer system or similar
electronic computing device manipulates and transforms data
represented as physical (electronic) quantities within the computer
system's registers and memories into other data similarly
represented as physical quantities within the computer system
memories or registers or other such information storage,
transmission, or display devices. The present invention is also
well suited to the use of other computer systems such as, for
example, optical and mechanical computers.
Computer System Environment of the Present Invention
With reference now to FIG. 1, portions of the present method and
system are comprised of computer-readable and computer-executable
instructions which reside, for example, in computer-usable media of
a computer system. FIG. 1 illustrates an exemplary computer system
100 used in accordance with one embodiment of the present
invention. It is appreciated that system 100 of FIG. 1 is exemplary
only and that the present invention can operate on or within a
number of different computer systems including general purpose
networked computer systems, embedded computer systems, routers,
switches, server devices, client devices, various intermediate
devices/nodes, stand alone computer systems, and the like.
Additionally, computer system 100 of FIG. 1 is well adapted having
computer readable media such as, for example, a floppy disk, a
compact disc, and the like coupled thereto. Such computer readable
media is not shown coupled to computer system 100 in FIG. 1 for
purposes of clarity. Additionally, portions of the present
embodiment are well suited to operating in conjunction with various
mobile clients such as, for example, a cell phone, personal digital
assistant (PDA), laptop computer, pager, and the like.
System 100 of FIG. 1 includes an address/data bus 102 for
communicating information, and a central processor unit 104 coupled
to bus 102 for processing information and instructions. As an
example, central processor unit 104 may be an IA-64 microprocessor
architecture by Intel Corporation of Santa Clara, Calif. System 100
also incudes data storage features such as a computer usable
volatile memory 106, e.g. random access memory (RAM), coupled to
bus 102 for storing information and instructions for central
processor unit 104. System 100 also includes computer usable
non-volatile memory 108, e.g. read only memory (ROM), coupled to
bus 102 for storing static information and instructions for the
central processor unit 104. Such static information is comprised,
in one embodiment, of commands for configuration and initial
operations of computer system 100. Computer system 100 also
includes a data storage unit 110 (e.g., a magnetic or optical disk
and disk drive) coupled to bus 102 for storing information and
instructions.
System 100 of the present invention also includes an optional
alphanumeric input device 112 including alphanumeric and function
keys coupled to bus 102 for communicating information and command
selections to central processor unit 104. System 100 also
optionally includes an optional cursor control device 114 coupled
to bus 102 for communicating user input information and command
selections to central processor unit 104. System 100 of the present
embodiment also includes an optional display device 116 coupled to
bus 102 for displaying information. System 100 of the present
embodiment also includes a communication interface 118 which
enables computer system 100 to interface with other computers or
devices. In one embodiment, communication 118 is, for example, a
modem, an integrated services digital network (ISDN) card or the
like, a local area network (LAN) port, etc. Those skilled in the
art will recognize that modems or various types of network
interface cards (NICs) typically provide data communications via
telephone lines, while a LAN port provides data communications via
a LAN. Communication interface 118 of computer system 100 may also
enable wireless communications. Furthermore, communication
interface 118 may enable communication with other computers or
devices through one or more networks. For example, computer system
100, using communication interface 118, may communicate to the
"Internet."
Computer system 100 may be used to implement the techniques
described below. In various embodiments, processor 104 performs the
steps of the techniques by executing instructions brought to RAM
106. In alternative embodiments, hard-wired circuitry may be used
in place of or in combination with software instructions to
implement the described techniques. Consequently, embodiments of
the invention are not limited to any one or a combination of
software, hardware, or circuitry.
Instructions executed by processor 104 may be stored in and carried
through one or more computer-readable media, which refer to any
medium from which a computer reads information. Computer-readable
media may be, for example, a floppy disk, a hard disk, a zip-drive
cartridge, a magnetic tape, or any other magnetic medium, a CD-ROM,
a CD-RAM, a DVD-ROM, a DVD-RAM, or any other optical medium,
paper-tape, punch-cards, or any other physical medium having
patterns of holes, a RAM, a ROM, an EPROM, or any other memory chip
or cartridge. Computer-readable media may also be coaxial cables,
copper wire, fiber optics, acoustic, or light waves, etc. As an
example, the instructions to be executed by processor 104 are in
the form of one or more software programs and are initially stored
in a CD-ROM being interfaced with computer system 100. Computer
system 100 loads these instructions in RAM 106, executes some
instructions, and sends some instructions via communication
interface 118, a modem, and a telephone line to a network, the
Internet, etc. A remote computer, receiving data through a network
cable, executes the received instructions and sends the data to
computer system 100 to be stored in storage device 110.
Referring still to FIG. 1, optional display device 116 of FIG. 1,
may be a liquid crystal device, cathode ray tube, or other display
device suitable for creating graphic images and alphanumeric
characters recognizable to a user. Optional cursor control device
114 allows the computer user to dynamically signal the two
dimensional movement of a visible symbol (cursor) on a display
screen of display device 116. Many implementations of cursor
control device 114 are known in the art including a trackball,
mouse, touch pad, joystick or special keys on alphanumeric input
device 112 capable of signaling movement of a given direction or
manner of displacement. Alternatively, it will be appreciated that
a cursor can be directed and/or activated via input from
alphanumeric input device 112 using special keys and key sequence
commands. The present invention is also well suited to directing a
cursor by other means such as, for example, voice commands. A more
detailed discussion of the present invention is found below.
General Method and System for Instrumenting a Virtual Function
With reference next to flow chart 200 of FIG. 2 and to FIG. 1,
exemplary steps used by the various embodiments of present
invention are illustrated. Flow chart 200 includes processes of the
present invention which, in one embodiment, are carried out by a
processor under the control of computer-readable and
computer-executable instructions. The computer-readable and
computer-executable instructions reside, for example, in data
storage features such as computer usable volatile memory 106,
computer usable non-volatile memory 108, and/or data storage device
110 of FIG. 1. In one embodiment, the computer-readable and
computer-executable instructions are used to control or operate in
conjunction with, for example, processor 104 of FIG. 1.
With reference again to FIG. 2, steps performed in accordance with
one embodiment of the present invention are shown. Although
specific steps are disclosed in flow chart 200 of FIG. 2, such
steps are exemplary. That is, the present invention is well suited
to performing various other steps or variations of the steps
recited in FIG. 2. At step 202, the present embodiment, determines
whether a virtual table exists for a virtual function. More
specifically, in one embodiment, an instrumenting process
(instrumentor) monitors a target process using, for example, the
debug interface. In this embodiment, the instrumentor monitors the
target process for mainly two events: the functions invoked in the
target process; and shared modules getting loaded and/or unloaded.
Since most compilers maintain virtual table information in the
symbol table, in the present embodiment, the instrumentor reads the
entire symbol table and knows the exact location of all virtual
tables when the module is loaded.
Referring still to step 202, in one approach, the instrumenting
application (i.e. the instrumentor) is comprised of the Caliper
application by Hewlett-Packard Company of Palo Alto, Calif. The
present invention is, however, well suited to use with various
other instrumenting applications. Also, in one embodiment,
processor 104 of FIG. 1 in conjunction with instructions, residing,
for example, in RAM 106, ROM 108, and/or data storage device 110,
comprise an apparatus which operates to perform step 202.
With reference next to step 204, the present embodiment determines
the call type for the virtual function. That is, by locating a
virtual table, the present embodiment establishes that the virtual
function can be called by a virtual function call. If there is no
virtual table corresponding to the virtual function, the present
embodiment establishes that the virtual function is called by a
non-virtual call (i.e. a direct function call or an indirect
function call). The present invention is, however, well suited to
use with various other instrumenting applications. Also, in one
embodiment, processor 104 of FIG. 1 in conjunction with
instructions, residing, for example, in RAM 106, ROM 108, and/or
data storage device 110, comprise an apparatus which operates to
perform step 204. Thus, the present embodiment provides a method
and system for determining the type of call made to the virtual
function.
With reference now to FIG. 3, a flow chart 300 of steps performed
in accordance with another embodiment of the present invention is
shown. The method of the present embodiment includes steps 202 and
204 of FIG. 2. These steps were described above in detail in
conjunction with the description of FIG. 2, and are not repeated
herein for purposes of brevity and clarity. The method of the
present embodiment as described in FIG. 3 also includes new step
302. At step 302, the present embodiment, performs instrumentation
on said virtual function based upon the call type determined in
steps 202 and 204. In one embodiment, if the call type is
determined to be non-virtual (i.e. a direct function call or an
indirect function call), the present embodiment performs a
conventional instrumentation process upon the virtual function
being called. On the other hand, if the call to the virtual
function is determined to be a virtual function call, the present
embodiment performs a novel instrumentation process. Various
embodiments of the novel instrumentation process performed by the
present invention are described below in detail. In one embodiment,
processor 104 of FIG. 1 in conjunction with instructions, residing,
for example, in RAM 106, ROM 108, and/or data storage device 110,
comprise an apparatus which operates to perform step 302.
With reference now to FIG. 4, a flow chart 400 of steps performed
in accordance with another embodiment of the present invention is
shown. The method of the present embodiment includes steps 202, 204
and 302 of FIG. 3. These steps were described above in detail in
conjunction with the description of FIGS. 2 and 3, and are not
repeated herein for purposes of brevity and clarity. The method of
the present embodiment as described in FIG. 4 also includes new
steps 402, 404 and 406. At step 402, provided that a virtual table
was located for the virtual function, the present embodiment
replaces an existing address for the virtual function with a new
address in the virtual table such that the new address points to
instrumentation code. Also, the present invention is well suited to
an embodiment in which the instrumentation code is dynamically
created, and to an embodiment in which the instrumentation code is
not dynamically created.
Still referring to step 402, in one embodiment, using the starting
address of each virtual table, the instrumentor loads the data
segment of the executable, which is where the virtual tables are
stored in one architecture, and reads the corresponding location in
the data segment to determine which functions are contained inside
each located virtual table. In one embodiment, because shared
libraries are relocated to new and varying addresses on loading of
the library, the present invention performs some pointer
manipulation to get the virtual address from the address stored in
the data segment of the shared library. In such an approach, this
offset (i.e. the pointer manipulation) is stored by the
instrumentor during the loading of the library.
At step 402, the instrumentor provides instrumentation code. More
specifically, in one embodiment, the instrumentor creates for each
virtual function found in the virtual tables a single bundle or
instruction in shared memory that only contains a breakpoint
instruction or other control transfer instruction. Additional
details related to instrumentation including discussion of features
such as breakpoints or other control transfer instructions,
branches, switch tables, procedure lookup tables (PLTs) can be
found in co-owned, commonly-assigned U.S. patent application Ser.
No. 09/833,248 filed Apr. 11, 2001, entitled "Dynamic
Instrumentation Of An Executable Program", to Hundt et al. which is
incorporated herein by reference as background material.
With reference still to step 402, the instrumentor of the present
embodiment stores the virtual table information read from the data
segment. The instrumentor then rewrites the virtual tables of the
target process with a modified virtual table which contains the
addresses of the breakpoints associated with each virtual function
instead of the original virtual function start address. In one
approach, the instrumentation code is comprised of an instruction
set which will surrender control of the target process to the
instrumentor.
Referring next to step 404, upon a call to the virtual function, in
the present embodiment, the target process loads the new address
from the virtual table such that execution is directed to the
instrumentation code. That is, when the target process makes a
virtual function call, it reads the contents of the virtual table
to get the function start address. In this embodiment, instead of
making an indirect call to the virtual function start address, the
target process makes an indirect call to the breakpoint (created at
step 402) which is intended to deliver control of the target
process to the instrumentor.
With reference now to step 406, in one embodiment, the present
invention then continues execution and executes the instrumentation
code such that control is delivered to the instrumentor. In one
embodiment, processor 104 of FIG. 1 in conjunction with
instructions, residing, for example, in RAM 106, ROM 108, and/or
data storage device 110, comprise an apparatus which operates to
perform steps 402, 404, and 406.
With reference now to FIG. 5, a flow chart 500 of steps performed
in accordance with another embodiment of the present invention is
shown. The method of the present embodiment includes steps 202,
204, 302, 402, 404, and 406 of FIG. 4. These steps were described
above in detail in conjunction with the description of FIG. 4, and
are not repeated herein for purposes of brevity and clarity. The
method of the present embodiment as described in FIG. 5 also
includes new steps 502 and 504. At step 502, the present embodiment
performs a desired task (e.g. an instrumentation task) by the
instrumentor. As an example, the present invention enables the
instrumentor to, for example, increment a variable representing the
virtual function. Although such specific examples are provided
herein, the present invention is also well suited to having the
instrumentor perform various other tasks.
With reference now to step 504, the present embodiment then resumes
execution by the instrumentor at the existing address previously
contained in the virtual table. That is, in this embodiment, the
instrumentor, without doing any further modification to the target
process, continues execution at the original virtual function entry
point. In one embodiment, processor 104 of FIG. 1 in conjunction
with instructions, residing, for example, in RAM 106, ROM 108,
and/or data storage device 110, comprise an apparatus which
operates to perform steps 502 and 504.
With reference now to FIG. 6, a flow chart 600 of steps performed
in accordance with another embodiment of the present invention is
shown. The method of the present embodiment includes steps 202,
204, 302, 402, 404, and 406 of FIG. 4. These steps were described
above in detail in conjunction with the description of FIG. 4, and
are not repeated herein for purposes of brevity and clarity. The
method of the present embodiment as described in FIG. 6 also
includes new steps 602 and 604. At step 602, the present embodiment
overwrites the instrumentation code with instrumentation code which
performs a desired instrumentation task. That is, in the embodiment
of FIG. 5, the instrumentor performs the desired instrumentation
task and then the instrumentor resumes execution at the existing
address previously contained in the virtual table. In the present
embodiment however, instrumentation code (e.g. probe code) is added
to the target process in the form of instructions which are written
over the instrumentation code. The instrumentation code, when
executed by the target process performs the desired instrumentation
task. In one embodiment, the instrumentation task comprises
incrementing a variable representing the virtual function. Although
such a specific example is provided herein, the present invention
is also well suited to providing instrumentation code which, when
executed, performs various other instrumentation tasks.
With reference still to step 602, in another embodiment, the
instrumentation code is provided at a new location. In one such
embodiment, the instrumentor must then overwrite all virtual table
entries associated with the virtual function to contain the address
of the instrumentation code instead of the breakpoint.
At step 604, the present embodiment provides an instruction at the
end of the instrumentation code wherein the instruction points back
to the existing address previously contained in the virtual table
or the address of an instrumented version of the function. In one
example, the instruction at the end of the instrumentation code is
comprised of a direct branch at the end of it to the virtual
function start address. Thus, the present embodiment does not
surrender or repeatedly transfer control of the target process to
the instrumentor. In one embodiment, processor 104 of FIG. 1 in
conjunction with instructions, residing, for example, in RAM 106,
ROM 108, and/or data storage device 110, comprise an apparatus
which operates to perform steps 602 and 604.
With reference now to FIG. 7, a flow chart 700 of steps performed
in accordance with another embodiment of the present invention is
shown. The method of the present embodiment includes steps 202 and
204 of FIG. 7. These steps were described above in detail in
conjunction with the description of FIG. 7, and are not repeated
herein for purposes of brevity and clarity. The method of the
present embodiment as described in FIG. 7 also includes new step
702. At step 702, the present embodiment As yet another example,
the present invention is also well suited to an embodiment which
determines from which location the virtual function has been
called. More specifically, in one embodiment, the instrumentor
determines the location from which the virtual function has been
called by examining the return pointer. Hence, the present
embodiment is able to provide such valuable information to the
programmer. In one embodiment, processor 104 of FIG. 1 in
conjunction with instructions, residing, for example, in RAM 106,
ROM 108, and/or data storage device 110, comprise an apparatus
which operates to perform step 702.
With reference now to FIG. 8, a flow chart 800 of steps performed
in accordance with another embodiment of the present invention is
shown. The method of the present embodiment includes steps 202,
204, 302, 402, 404, and 406 of FIG. 4. These steps were described
above in detail in conjunction with the description of FIG. 4, and
are not repeated herein for purposes of brevity and clarity. The
method of the present embodiment as described in FIG. 8 also
includes new steps 802. At step 802, the present embodiment
maintains a mapping between the existing address for the virtual
function and the new address for the virtual function. In so doing,
the present embodiment enables the functionality recited above in
step 402. That is, by maintaining a mapping between the existing
address for the virtual function and the new address for the
virtual function, the present embodiment enables the replacing of
the existing address of the virtual function with the new address
of the virtual function and also replacing of the new address of
the virtual function with the existing address of the virtual
function.
Hence, the present invention provides in various embodiments,
accurate analysis of the number and type of virtual function calls
and their callers. Such information is extremely valuable to
software developers using object-oriented languages. Since virtual
function calls are slower than direct function calls, by presenting
this information to the developer the present invention helps gauge
whether the software should be altered to change the virtual
function call to a non-virtual function call. In an instrumentation
tool which relocates the instrumented function into shared memory,
various embodiments of the present invention achieve an actual
performance improvement because without rewriting the virtual
tables for the new function location, a virtual function call is
made to the start address of the original function. The original
function is then structured to make a long branch to the start of
the instrumented function in shared memory. Hence, only one (i.e.
the first) virtual function call is made in such embodiments.
Thus, the present invention provides a method and system for
instrumenting a virtual function including determining the type of
call made to the virtual function.
The foregoing descriptions of specific embodiments of the present
invention have been presented for purposes of illustration and
description. They are not intended to be exhaustive or to limit the
invention to the precise forms disclosed, and obviously many
modifications and variations are possible in light of the above
teaching. The embodiments were chosen and described in order to
best explain the principles of the invention and its practical
application, to thereby enable others skilled in the art to best
utilize the invention and various embodiments with various
modifications as are suited to the particular use contemplated. It
is intended that the scope of the invention be defined by the
claims appended hereto and their equivalents.
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